1. Technical Field
The invention disclosed herein relates generally to power generation through the use of wind turbines, and more particularly to providing apparatuses and methods for diverting wind so as to increase the flow of wind supplied to the blades of a wind turbine and thus increasing the power generated by the action of the blades.
2. Background Art
The conversion of wind energy into electrical energy is well known. The most common apparatus for converting wind energy into useful power is the wind turbine which typically includes a plurality of blades directly exposed to the wind which are connected to a central hub and rotate about a common horizontal axis.
In older designs of wind turbines, the horizontal axis is permanently aligned with the prevailing wind direction. As a result, the efficiency is reduced when the wind changes from the prevailing direction. In newer and more advanced wind turbine designs, the horizontal axis of the rotor will turn into the wind, either rotating freely to align with the wind or is driven by servomotors.
Although wind turbines are a well known method for harnessing wind energy, they suffer from several inherent disadvantages. Firstly, the rotors must be positioned on tall towers both to capture the faster wind speeds at higher elevations but also to avoid the undesirable effects of air turbulence caused by obstructions at ground level.
Additionally, wind turbines are only able to effectively extract energy from a circular cross section of the airstream. A substantial portion of the airstream passes under, over, and around the area swept by the rotor, limiting its capacity to extract all of the power available from the surrounding wind. Further, large scale wind turbines are only able to start operating in moderately high wind speeds of approximately 7 to 10 miles per hour (“MPH”). This wind speed is not always available, which means that the wind turbine will sit idle and not be able to start operating until such time as the wind speed picks up and reaches the minimum threshold starting speed.
Another limiting factor for large scale wind turbines is that the current design is approaching maximum size. Rotor length is restricted by the material of construction: i.e., aluminum, fiberglass or carbon fiber. The longer the rotor blades, the heavier. Beyond a certain length, they are too long and too heavy to be self supporting. This then becomes the maximum size/power output for a given wind turbine installation.
Some of the original wind farms that were installed positioned the turbines on ridges to take advantage of the natural topography to increase the wind speed going to the rotor and thereby the energy output. In addition, it is possible to position a turbine in a valley between two (2) hills to also take advantage of this natural venturi effect. However, few naturally occurring locations have the correct terrain to produce laminar airflow and to minimize air turbulence while at the same time maximizing the wind speed. If such locations do exist, they often are facing the wrong direction to take advantage of the prevailing wind or are blocked when the wind shifts. Lastly, even if the natural topography is suitable, the location may be too far away to economically tie a remotely located wind turbine into an existing power grid.
A further problem for small scale wind turbines, although ideally sized for some applications such as roof mounting on buildings, is that they are not as efficient as large sized turbines. In addition, due to extreme turbulence at the building parapet and over the top of the building itself, small turbines are only able to produce limited amounts of power.
It has long been recognized that the efficiency of a wind turbine could be improved by directing more wind onto the turbine itself. One of the earliest recorded methods of doing this was the Persian Panemone, a type of vertical axis wind turbine with its axis positioned at 90 degrees to the direction of the wind with the blades moving parallel to the wind. The Persian Panemone consisted of four (4) sails on a vertical axle which turned when the wind blew. The vanes or sails moving upwind had to be blocked by a wall to prevent them from being blown back. As a result, half of the turbine was shielded by the wall, thereby reducing its efficiency.
More recent attempts at concentrating the wind involved shrouds or diffusers or ducted inlets, all names for basically the same design which takes advantage of the venturi effect. Some initial research for these designs was performed by NASA in 1957 as reported in the document “Experimental Investigation of Lift, Drag and Pitching Moment of Five Annular Airfoils”. Further studies were conducted throughout the 1960's and 1970's. In the 1990's a full scale device was built by a New Zealand company called Vortec.
As recently as Feb. 3, 2009, U.S. Pat. No. 7,484,363 to Reidy et al. was issued for a venturi type augmenter that completely enshrouds the turbine rotor.
These types of augmentation devices used on wind turbine installations where the rotor turns into the direction of the wind have not proved very successful due to a variety of factors. The main problem is that the opening of the diffuser needs to be exactly in line with the incoming wind. If out of alignment, the shroud will block the airstream. In addition, it was found that even slight misalignment between the throat of the diffuser and the direction of the wind causes the air flow to go from laminar to turbulent, greatly reducing the efficiency.
Designs to prevent this misalignment have included mounting the diffuser on the yaw mechanism that orients the rotor in the direction of the wind. This greatly complicates the design of the support tower and the yaw mechanism required to rotate both the diffuser and the rotor itself. It was found on the turbines with built-in diffusers, that it is quite difficult to rotate the assembly fast enough to maintain the correct alignment.
U.S. Pat. No. 6,755,608 to Boughton (“Boughton”) discloses emplacing a wind power generation apparatus either on top of, or adjacent to, a natural or artificial mound so as to increase the height of the wind power generation apparatus and provide some focus of the wind on the turbine rotor of the apparatus. Boughton also discloses the emplacement of wind power generation apparatuses so as to take the greatest advantage of artificial mounds, such as those created by piling up refuse in a landfill. In addition, in Boughton, support towers upon which the wind power turbine towers are emplaced may be installed with collapsible supports such as a jacking mechanism or a telescoping support tower. Boughton also discloses an inflatable structure either together with supports or separately constructed, such that the support towers may be raised as the artificial mound grows. The system of Boughton may also contain a hinge at the base of the wind power turbine to provide for ease of access when maintenance on the wind turbine itself is required.
The prior art system as disclosed in Boughton has numerous disadvantages. An initial disadvantage is the requirement for reinforcement of the artificial mound to support the weight of the wind power generation apparatus on top of the artificial mound. Wind power generation systems are often quite large, as seen in the example of a wind power generation system installed in Bowling Green, Ky. where the wind power generation unit stands 256 feet tall with a blade length of 134 feet. Thus, supporting the weight of an apparatus of this size on top of an artificially produced mound would require some careful engineering with regard to materials and stability of the finished mound configuration. Engineering of this complexity would increase both the time of construction and cost of such a mound significantly.
Another disadvantage of the system disclosed in Boughton is that attempting to add a mound to already existing wind power generation emplacements would be even more costly in terms of engineering and construction due to the need to first remove the existing installation, build the mound, then reinstall the wind power generation unit. The return on investment in such an installation based upon the increase in power generation sales would be so long as to render such a retrofit economically unfeasible.
An additional disadvantage of the prior art system as disclosed in Boughton is that the area from the top of the mound to the bottom of the blade of the wind generation turbine is open. This open area allows for the escape of wind accelerated by the mound by passing through the open area without doing any work pushing against the rotor blades.